Definitely check the hop rubber. I'd look at changing it to a Maple Leaf Macaron 60 or MR Hop 60 with the Omega nub as well. ZCI make barrels that will fit (M14 hop units have the locking clip cutouts in a different place so don't just buy any old barrel). Bear in mind that going to a tighter bore barrel WILL increase your FPS (it's happened on every Cyma M14 I've done it to). @ak2m4 carries the right sort of length but he's out of stock right now https://www.ak2m4.co.uk/internal-parts/inner-barrels/zci-inner-barrel-550mm.
To be fair, the stock inner barrel is fine, give it a good clean and swap out the hop rubber first and see how you get on.
One of my first pistols was the socom gear M9A1. The slide fit like a dick in a shirt sleeve and gas efficiency was almost as bad as a 1911 in the winter. I don't think it ever locked back on an empty mag, although the day I put Guarder Power Up gas in it and got 400fps on the chrono was hilarious!
Take off stock and place in bag. Desperately try to find the pins when you get to site.
Play all day with no stock and the battery taped to the side of the receiver.
Find pins in your pocket when you get home.
I have an old ASG B&T tracer unit that has a cracked battery cover held on with electrical tape and it STILL works after at least 8 years of abuse. It may not be USB chargeable or vomit rainbows but it still works....
I bought a chest rig from Taiwangun via Patrolbase and it was absolutely fine. Just email [email protected] with what you want and they'll sort it. You may have to wait a bit because of TWG shipping things in bulk to cut costs. Price wise though it was pretty close to what they advertise on the TWG website.
As for "it's just airsoft stuff" - as far as HMRC are concerned that is totally irrelevant. It's importing taxable goods.
I have a Vector Optics magnifier which is pretty good but the Element/Aim-O one I have is my go to (also in a FTC mount). Clear, adjusts well, cheap. Job jobbed.
I mean...paint stripper is made to strip paint so....
Brake fluid will do the job but probably not quite as well as something designed for the task. Scrubbing/rubbing/agitating (call it what you will) will help but make sure you wear decent gloves.
Make sure you properly wash the brake fluid off too, otherwise you'll have problems with paint adhesion when you respray it.